It is known that immune response to certain antigens which are otherwise weakly immunogenic can be enhanced through the use of vaccine adjuvants. Such adjuvants potentiate the immune response to specific antigens and are therefore the subject of considerable interest and study within the medical community.
Research has permitted development of vaccines possessing antigenic epitopes that were previously impossible to produce. For example, currently available vaccine candidates include synthetic peptides mimicking streptococcal, gonococcal, and malarial antigens. These purified antigens are generally weak immunogens, however, that require adjuvants in order to evoke protective immunity. However, conventional vaccine adjuvants possess a number of drawbacks, which limit their overall use and effectiveness.
It is also common knowledge that substances, which stimulate immune cells in vitro exhibit similar immuno-stimulatory effects in vivo. These compounds, such as recombinant cytokines, pathogen products (e.g. toxins, lipids, proteins/peptides, carbohydrates and nucleic acids) and other mammalian-derived immunostimulatory molecules (e.g. heat shock proteins, complement, immune complexes and proteoglycans) all induce a measurable pro-inflammatory response both in vitro and in vivo.
Historically, the classic adjuvants have been Freund's complete or incomplete (i.e., without mycobacteria) adjuvants. Edmund Coley, the inventor of Coley's Toxin, described this potential for cancer immuno-therapy.
Other adjuvants have been compared to Freund's. However, clinical use of such adjuvants in animals or humans is precluded because they produce granulomas at the site of injection; fever and other toxic effects; and tuberculin hypersensitivity. Other materials, such as mineral oil and aluminum hydroxide, have also been used as adjuvants, but they invariably suffer from disadvantages. For example, mineral oil is known to produce tissue irritation and to be potentially oncogenic. Aluminum hydroxide, the only approved adjuvant in the United States, also induces granulomas at the inoculation site and furthermore it does not effectively induce cell-mediated immunity. Moreover, many of the adjuvants currently available have limited utility because they contain components, which are not metabolizable in humans. Additionally, most adjuvants are difficult to prepare in that they may require time consuming procedures and the use, in some cases, of elaborate and expensive equipment to formulate a vaccine and adjuvant system.
For a thorough discussion of various immunological adjuvants, see “Current Status of Immunological Adjuvants”, Ann. Rev. Immunol., 1986, 4, pp. 369-388, and “Recent Advances in Vaccine Adjuvants and Delivery Systems” by Derek T O'Hagan and Nicholas M. Valiente, both of which are hereby incorporated by reference in its entirety. See also U.S. Pat. Nos. 4,806,352; 5,026,543; and 5,026,546 for disclosures of various vaccine adjuvants appearing in the patent literature all of which are hereby incorporated by reference in its entirety.
There has been an effort to find new adjuvants for vaccines that would overcome the drawbacks and deficiencies of conventional adjuvants. In particular, an adjuvant formulation which elicits potent cell-mediated and humoral immune responses to a wide range of antigens in humans and domestic animals, but lacking the side effects of conventional adjuvants, such as Freund's complete adjuvant, would be highly desirable.
It is also desirable to identify small molecules, which stimulate a proinflammatory response for use as vaccine adjuvants.
Hepatitis is a systemic disease, which predominantly affects the liver. The disease is typified by the initial onset of symptoms such as anorexia, nausea, vomiting, fatigue, malaise, arthralgias, myalgias, and headaches, followed by the onset of jaundice. The disease may also be characterized by increased serum levels of the aminotransferases AST and ALT. Quantification of these enzymes in serum indicates the extent of liver damage.
There are five general categories of viral agents which have been associated with hepatitis: the hepatitis A virus (HAV); the hepatitis B virus (HBV); two types of non-A, non-B (NANB) agents, one blood-borne (hepatitis C) and the other enterically transmitted (hepatitis E); and the HBV-associated delta agent (hepatitis D).
There are two general clinical categories of hepatitis, acute hepatitis and chronic hepatitis. Symptoms for acute hepatitis range from asymptomatic and non-apparent to fatal infections. The disease may be subclinical and persistent, or rapidly progress to chronic liver disease with cirrhosis, and in some cases, to hepatocellular carcinoma. Acute hepatitis B infection in adult Caucasians in the United States progresses to chronic hepatitis B in about 5% to 10% of the cases. In the remainder of the cases, approximately 65% are asymptomatic. In the Far East, infection is usually perinatal, and 50% to 90% progress to the chronic state. It is likely that the different rates of progression are linked to the age at infection rather than genetic differences in the hosts. In the United States, about 0.2% of the population is chronically infected, with higher percentages in high-risk groups such as physicians, drug addicts and renal dialysis patients. In countries such as Taiwan, Hong Kong and Singapore, the level in the population with hepatitis infection may be as high as 10%.
In the United States, about 20% of patients with chronic hepatitis die of liver failure, and a further 5% develop hepatitis B-associated carcinoma. In the Far East, a large percentage of the population is infected with HBV, and after a long chronic infection (20 to 40 years), approximately 25% of these will develop hepatocellular carcinoma.
After the development of serologic tests for both hepatitis A and B, investigators identified other patients with hepatitis-like symptoms, and with incubation periods and modes of transmission consistent with an infectious disease, but without serologic evidence of hepatitis A or B infection. After almost 15 years, the causative agent was identified as an RNA virus. This virus (designated “hepatitis C”) has no homology with HBV, retroviruses, or other hepatitis viruses.
Hepatitis C(HCV) appears to be the major cause of post-transfusion and sporadic non-A, non-B (NANB) hepatitis worldwide, and plays a major role in the development of chronic liver disease, including hepatocellular carcinoma (Kuo et al., Science 244:362-364, 1989; Choo et al., British Medical Bulletin 46(2):423441, 1990). Of the approximately 3 million persons who receive transfusions each year, approximately 150,000 will develop acute hepatitis C (Davis et al., New Eng. J. Med. 321(22):1501-1506, 1989). In addition, of those that develop acute hepatitis C, at least one-half will develop chronic hepatitis C.
Until recently, no therapy has proven effective for treatment of acute or chronic hepatitis B or C infections, and patients infected with hepatitis must generally allow the disease to run its course. Most anti-viral drugs, such as acyclovir, as well as attempts to bolster the immune system through the use of corticosteroids have proven ineffective (Alter, “Viral hepatitis and liver disease,” Zuckerman (ed.), New York: Alan R. Liss, pp. 537-42, 1988). Some anti-viral activity has been observed with adenosine arabinoside (Jacyna et al., British Med. Bull. 46:368-382, 1990), although toxic side effects, which are associated with this drug render such treatment unacceptable.
One treatment that has provided some benefit for chronic hepatitis B and C infections is the use of recombinant alpha interferon (Davis et al., New Eng. J. Med. 321(22):1501-1506, 1989; Perrillo et al., New Eng. J. Med. 323:295-301, 1990). However, for patients with hepatitis B infections only about 35% of infectees responded to such treatment, and in perinatal infectees only about 10% responded to treatment. For hepatitis C infections, despite apparent short-term success utilizing such therapy, six months after termination of treatment half of the patients who responded to therapy had relapsed. In addition, a further difficulty with alpha interferon therapy is that the composition frequently has toxic side effects such as nausea, and flu-like symptoms, which require reduced dosages for sensitive patients.
A disease related to hepatitis B and hepatitis C infections is hepatocellular carcinoma. Briefly, hepatocellular carcinoma is the most common cancer worldwide. It is responsible for approximately 1,000,000 deaths annually, most of them in China and in sub-Saharan Africa. There is strong evidence of an etiologic role for hepatitis B infection in hepatocellular carcinoma. Carriers of the HBV are at greater than 90 times higher risk for the development of hepatocellular carcinoma than noncarriers. In many cases, hepatitis B virus DNA is integrated within the cellular genome of the tumor. Similarly, hepatitis C virus has also recently been found to be associated with hepatocellular carcinoma, based upon the observation that circulating HCV antibodies can be found in some patients with hepatocellular carcinoma. At present, surgical resection offers the only treatment for hepatocellular carcinoma, as chemotherapy, radiotherapy, and immunotherapy have not shown much promise (Colombo et al., Lancet 1006-1008, 1989; Bisceglie et al., Ann. of Internal Med. 108:390401, 1988; Watanabe et al., Int. J. Cancer 48:340-343, 1991; Bisceglie et al., Amer. J. Gastro. 86:335-338, 1991).
Therefore, therapeutics that could serve to augment natural host defenses against hepatitis, or against tumor induction and progression, with reduced cytotoxicity, or that allows treatment of interferon non-responsive individuals would be very beneficial. The present invention provides such therapeutic agents, and further provides other related advantages.